Cdi choices

[FurryOnTheInside]

@ butre:
Jees! For the layman that's a lot of factors to account for when you only get one setting and one chance to get it right. I'd be scared to pull the trigger on a purchase like that..
As far as this layman can understand from the forums, more advance means it suits either a slower burn (from lower compression) or a faster rpm (piston downstroke to get it away from the battering). I had really already made my mind up based on the other issues, but that (if I'm even understanding correctly) confirms it for me about the technical side anyway.

 

[Deleted member 12676]

yeah, the topic of CDI is truly technical.
actually because of increased turbulence at high RPM the timing needs to change from advanced to retarded because the mixture burns faster. that also takes into account that at high rpm the time from TDC to exhaust opening is less.
an expansion chamber increases the dynamic compression at high rpm so that the timing needs to be even more delayed (retarded) whilst the reverse pressure waves are stuffing the escaping fuel mixture back into the cylinder.

 

[FurryOnTheInside]

(another Jeesh!)
I don't fancy tuning an engine to suit the needs of a single unchangeable CDI setting. Forget that. Makes sense to tune the CDI to the individual engine. (and talking to the man who designed it, how much better is that?!)

 

[butre]

that's why I use the jaguar on bikes that turn under 10k RPM (which really is too much for the stock needle bearing anyway, and unless you really know your way around a 2 stroke the most you might hit is 8500)

for race bikes that turn over 10k (mine turns 11,500-ish) I use the stock CDI in conjunction with an adjustable timing magnet. tune it for high RPM because it doesn't spend much time down low. it's cheaper than a good CDI anyway, though power down low can be a bit on the miserable side, but pedaling makes more torque than the motor does so you don't lose too much that way. if you feather the clutch right you can hold it in the power band until you're up to speed as well.

 

[Rob H]

Wow now we got us some info thanks fellas I guess maybe I was on to something I looked into it but was way to complicated for this Yankee so I'll go with the jaguar

 

[Rob H]

I like the idea of changing the timing curve as I keep experimenting with different carbs heads pipes and piston designs oh and gearing I finally got to put the triple range stack together I took it for a couple spins now I have to fine tune the shifting on front derailier